1. Field of the Invention
The invention relates to a method for determining an optical write power. In addition to a prior Inner Power Calibration Area, the method includes an Outer Power Calibration Area implementation on the outer area of a Readable/Writable Optical disc with a constant linear velocity (CLV) format and chooses the Inner Power Calibration Area or the Outer Power Calibration Area to calibrate the write power to ensure its accuracy.
2. Description of the Related Art
With the advance of electronics techniques and relative costing down, optical storage devices, for example, CD-R/CD-RW drives and the like, are widely used in computer systems and have increasingly become a standard peripheral. Generally, such drives perform an optical power calibration before data is written. The optical power calibration essentially pre-writes specific data to an Inner Power Calibration Area on an optical disc and reads it out to detect the feature of the optical disc, thereby determining the required write power to ensure the data is written into the optical disc properly.
FIG. 1 is a schematically lateral cross-section of a typical optical disc 10. The typical optical disc 10 includes a center 12, a power calibration area 14, a data storage area 16 and a last possible lead-out area 18. The area 14 is located on the inner area of the disc 10 (i.e., the outer area of the center 12) for an optical power calibration; the area 18 is located on the outer area (or the outer edge) of the disc 10 to record a data-end message of the disc 10; the area 16 is located between the areas 14 and 18 for a user data record.
For an optical disc with a CLV format, for example, Optical disc Write Once (CD-WO) and the like, a relative motion velocity of an optical head of an optical disc drive to an optical disc is kept at a constant velocity when data is written or read, regardless of the read/write position (i.e., a radius of the optical head on the optical disc) on the optical disc.
FIG. 2 is a diagram of two angular velocity-to-radius (W-R) curves of a optical disc with CLV format. FIG. 3 is a diagram of two linear velocity-to-radius (V-R) curves of the optical disc with CLV format.
When a lower linear velocity V1 is used to read/write data from/to an optical disc with CLV format, an angular velocity-to radius (W-R) curve CLV1 is shown in FIG. 2, wherein the angular velocity W is rotation speed of a servomotor in a CD drive and the radius R corresponds to the optical disc with CLV format. Due to the feature of constant linear velocity (CLV) in the optical disc with CLV format, the rotation speed (angular velocity) of the servomotor has to be increased as the radius to be written to (or read from) the optical disc is reduced (FIG. 2), in order to maintain the CLV write (or read) in any position of the optical disc. For example, when data on an outer area (such as at the position of radius R2) of the optical disc is written or read, the required angular velocity is W2. As well, when data on an inner area (such as at the position of radius R1) of the optical disc is written or read, the required angular velocity is W1 to keep the CLV (V1), wherein W1>W2.
As cited above, the typical power calibration is performed only in the Power Calibration Area. Because the Power Calibration Area is located on the inner area (where the accurate position has a radius RPC smaller than R1), the optical disc has to be provided with a higher angular velocity Wpcl to keep the same CLV (such as 12×) during the power calibration on the Power Calibration Area.
Basically, the design limit of an optical drive mechanism is increasingly reached as the rotation speed of the optical disc drive servomotor gets higher and higher. This increases vibration and further reduces power calibration reproducibility at high speeds, leading to errors. Generally, in the design practice of the optical disc drive, when a rotation speed (i.e. the angular velocity W of optical disc) exceeds a limit, the power calibration reliability cannot be obtained in the Power Calibration Area. The limit is referred to as an Optical Power Calibration (OPC limit) limit.
The OPC limit in FIG. 2 is WL. Upon the optical disc access at V1, the power calibration is not affected because the required rotation speed thereof is still smaller than the limit WL.
When a higher CLV V2 (such as 24×, i.e. an access velocity of 3600KB/sec) as shown in the curve CLV2 of FIGS. 2 and 3 is chosen, the required rotation speed for the power calibration in the Power Calibration Area (at the position of radius RPC) is increased to the velocity WPC2. Because the velocity WPC2 exceeds the limit WL, the power calibration may result in the increasing possibility of error. Thus, the optical disc drive is not able to perform the power calibration at V2 and provide some functions, for example a write choice at V2.